1. Field of the Invention
This invention relates to silicone rubber covered electrical conductors, and in particular, a silicone rubber covered electrical conductor which is characterized by the fact that a metallic conductor is covered with a composition of specific components and vulcanized to a silicone rubber.
2. Description of the Prior Art
Because silicone rubber is an exceptionally useful substance, being an electrical insulator and long lasting, it has conventionally been used as a material for covering electrical conductors. In general, silicone rubber covered electrical conductors are manufactured by extruding a rubber forming composition over an electrical conductor with an extruder and then curing the rubber forming composition by heating. It is normal practice to post cure the cured, insulated conductor, a second heat treatment, to remove the decomposition residues of the vulcanizing agents and to improve the electrical insulating properties. However, in the process of this second heat treatment, the cured silicone rubber layer and the electrical conductor adhere to one another. This adhesion becomes important when the ends of the electrical conductor are to be connected, because it is difficult to strip the silicone rubber layer from the end of the electrical conductor and silicone rubber residue remains on the conductor. Therefore, when the ends of such electrical conductors are connected, the contact is poor between the conductors which causes inferior electrical flow.
Conventionally, in removing the decomposition residues, the treatment conditions of the second heating have been inappropriately long at low temperatures, or short at high temperatures. This has been a rather great deterrent in the manufacture of silicone rubber covered electrical conductors.
In Canadian Pat. No. 872,303, issued Jan. 1, 1971, Compton described heat vulcanizable silicone rubber compositions which released from metal surfaces when they contained from 0.05 to 2 parts by weight of a metal salt of a carboxylic acid. An example shows zinc stearate as release agent and 2,5-bis-(tert-butylperoxide)-2,5-dimethylhexane as catalyst. Compton teaches that the compositions will release from a metal mold after vulcanization in the mold and the molded silicone rubber part can be removed without the use of a mold release material.
U.S. Pat. No. 4,145,505, issued Mar. 20, 1979, to Endstra teaches a cross-linkable composition consisting essentially of an organopolysiloxane and bis(o-chlorobenzoyl)peroxide. The composition is cross-linked by heating.